One of the books I'd suggest is on the list that abundi mecklo linked to:
"Earth Abides" written by George R. Stewart. Wonderful book, and one I've read over and over.
The other one that springs to mind is "Roadside Picnic" written by Arkady and Boris Strugatsky. A little odder maybe, and quite short, but brimming with ideas.
Both of them were re-released over here in the UK a couple of years ago, under the SF Masterworks banner, don't know if they were in the USA as well. If you see them though, they're both well worth a read.
The final one, and probably my favourite (though a lot harder to get over here, might be easy over there) is "Damnation Alley" written by Roger Zelazny. Great fun, and you can see how Carpenter's "Escape From New York" (and LA) were influenced by it.
On top of the ones people have already mentioned, that should keep you busy for a bit